1. Field of the Invention
The invention relates to a heat exchanger for an air conditioner, and more particularly to a heat exchanger having a plurality of louver patterns above and below heat exchanging tubes perpendicularly passing through flat fins whereby the air currents flowing therethrough become turbulent and mixed and further a dead air region around each tube is reduced.
2. Description of the Prior Art
A conventional heat exchanger for an air conditioner includes, as shown in FIG. 1, a plurality of flat fins 1 arranged in a parallel relation to each other at predetermined intervals and a plurality of heat exchanging tubes 2 passing through the fins 1 perpendicular thereto. The air currents flow in the space defined between the fins 1 in the direction of the arrow in FIG. 1 and exchange heat with the fluid flowing in the heat exchanging tubes 2.
For a thermal fluid flowing around each flat fin 1, it has been known that the thickness of the thermal boundary layer 3 on both heat transfer surfaces of the fin 1 is gradually thickened in proportion to square root of the distance from the air current inlet end of the fin 1 as shown in FIG. 2. In this regard, the heat transfer rate of the fin 1 is remarkably reduced in proportion to the distance from the air current inlet end. Therefore, the above heat exchanger has a lower heat transfer efficiency.
For the thermal fluid flowing about each heat transfer pipe 102, it has been also known that, when lower velocity air currents flow in the direction of the arrow of FIG. 3, the air currents separate from the outer surface of the pipe 2 at portions spaced apart from the center point of outer surface of the pipe 4 at angles of 70-degree to 80-degree. Therefore, a dead air region 4 is formed behind each tube 2 in a direction of the air flow as shown in the hatched region of FIG. 3. In the dead air region 4, the heat transfer rate of the tube 2 is remarkably reduced so that the heat transfer efficiency of the above heat exchanger becomes worse.
In order to overcome the above problems, there has been proposed another solution as illustrated in FIGS. 4 and 5. This heat exchanger includes a plurality of heat exchanging tubes 2 which are fitted into the regularly spaced flat fins 1 such that the tubes 2 are perpendicular to the fins 1. The heat exchanger also includes a plurality of rectangular louver patterns P which are formed adjacent the tubes 2 passing through each fin 1, without any fin portions disposed between the tubes 2. Each louver 5a, 5b, 5c, 5d, or 5e is formed by bending at a given angle the louver's outer edges relative to the plane of the flat fin 1, respectively, by way of the cutting process. Also, the louvers are vertically positioned to the heat exchanging tubes 2.
The above-described louvers 5a, 5b, 5c, 5d and 5e make the air flow turbulent. This operation advantageously reduces the thickness of the thermal boundary layers formed on the fins 1. However, since upper and lower ends of each pattern of louvers are parallel to a tangent of the outer circumferential surface of the tube 2 and the patterns of louvers are generally rectangular, a dead air region still exists behind each tube 2 in a direction of the air flow. Also, there is a problem in that unmixed air currents flow in the spaces between the plurality of flat fins 1, and the expected improvement of the heat transfer effect due to mixing of air currents cannot be guaranteed.
Further, there is a problem in that said upper and lower edges of said louvers 5a to 5e are arranged in parallel relation to the air current flow S, resulting in an increased pressure drop that reduces the heat transfer performance.